The invention relates to a fuel storage system for storing dimethylether (DME), blends thereof, or other similar highly volatile fuels, such as LPG (liquefied petroleum gas), propane, butane, on a vehicle. The fuel storage system comprises a main storage tank, an expansion tank, a fuel filling receptacle configured to receive a fuel filling nozzle of a filling station, and a valve arrangement having at least a normal operating setting and fuel filling setting. The valve arrangement provides a fuel passage between the main storage tank and the expansion tank in the normal operating setting, and the valve arrangement provides a fuel passage between the fuel filling receptacle and the the thin storage tank in the fuel filling setting.
The fuel storage system is particularly suitable for storing and supplying DME fuel. The combustion engine is preferably of the compression-ignition type, such as a diesel engine. The engine is preferably provided in a heavy vehicle, such as a heavy truck, a construction vehicle, a bus or a boat, but the invention is not limited to these vehicle types and may also be used for automobiles or fixed engine installations, such as power source for a fixed electrical generator or fixed hydraulic pump.
Rising prices of crude oil-derived fuel and fears of its effect on our climate as well as of its imminent shortages have led to further developments in production processes of alternative fuels and internal combustion engines for their use. One potentially important renewable fuel that can be effectively produced from a variety of stocks including biomass is dimethylether (DME) or other similar highly volatile fuel. With its soot-free combustion and high cetane number, DME is very well suited for diesel type internal combustion processes. However, DME has certain drawbacks in terms of fuel storage on a vehicle compared with conventional fuels like diesel and gasoline. Document U.S. Pat. No. 6,016,834 discloses a fuel storage system designed for storing propane as a fuel on a vehicle.
One drawback with DM E or DME-like fuels is that a significantly larger fuel volume needs to be stored for the vehicle to attain a certain mileage per single fill-up. Many types of vehicles have quite limited continuous space for a larger fuel tank installation, which then effectively limits the driving range. The problem is exacerbated by the relatively high thermal expansion coefficient of DME-like fuels, which usually further limits the effective volume of fuel that can be stored in a single tank.
DME, some blends thereof and similar highly volatile fuels, such as LPG (liquefied petroleum gas), propane, butane, etc. have a relatively high thermal expansion coefficient. That means that the volume of a certain amount of liquid fuel increases (expands) significantly when the temperature of the liquid fuel increases. This must be taken into account when the fuel is stored in a vehicle that is designed to operate in a relatively large ambient temperature range, such as typically from about −40° C. up to +50° C. Direct exposure of the fuel tank to sun light can additionally drive the temperature of the fuel stored within the tank even higher. Filling up the entire storage volume of a fuel tank with relatively cold liquid DME fuel and subsequently allowing the fuel to heat up within the fuel tank will thus generate a significant pressure increase within the fuel tank, which therefore risks bursting the tank and/or bleeding of fuel into the atmosphere.
One attempt to increase the effective volume of the fuel storage tank is known from U.S. Pat. No. 6,016,834, where an expansion tank capable of relieving possible overpressure in the main tank due to thermal expansion of the fuel is provided, and thus enabling a more complete filling up of the main tank. However, this particular prior art system fails to ensure a fail-safe and reliable enough system that would be adequately protected against human error and/or valve wear and filling station parameter variability potentially causing over-filling of the expansion tank, safety and vehicle reliability-related issues, and environmental pollution.
It is desirable to provide a fuel storage system and method for refuelling a fuel storage system for DME fuel or other similar highly volatile fuel, which fuel storage system and method provides improved safety in connection with refuelling of the fuel storage system.
According to a first aspect of the invention, a fuel storage system is provided. The fuel storage system is suitable for storing dimethylether (DME) or other similar highly volatile fuel on a vehicle. The fuel storage system comprises a main storage tank, an expansion tank, a fuel filling receptacle configured to receive a fuel filling nozzle of a filling station, and a valve arrangement having at least a normal operating setting and a fuel filling setting, wherein the valve arrangement in the normal operating setting provides a fuel passage between the main storage tank and the expansion tank, and wherein the valve arrangement in the fuel filling setting both provides a fuel passage between the fuel filling receptacle and the main storage tank and prevents fuel flow between the main storage tank and the expansion tank, wherein the fuel storage system is configured to mechanically prevent disconnection of the fuel filling nozzle from the fuel filling receptacle unless the valve arrangement is in the normal operating setting.
According to a second aspect of the invention, a method for refuelling a fuel storage system is provided. The fuel storage system comprises a main storage tank, an expansion tank, a fuel filling receptacle configured to receive a fuel filling nozzle of a filling station, and a valve arrangement having at least a normal operating setting and a fuel filling setting, wherein the valve arrangement in the normal operating setting provides a fuel passage between the main storage tank and the expansion tank, and wherein the valve arrangement in the fuel filling setting both provides a fuel passage between the fuel filling receptacle and the main storage tank and prevents fuel flow between the main storage tank and the expansion tank. The method comprising inserting the fuel filling nozzle into the fuel filling receptacle; locking the fuel filling nozzle in the fuel filling receptacle, such that the fuel filling nozzle is mechanically prevented from disconnection from the fuel filling receptacle, wherein the valve arrangement automatically is set in the fuel filling setting; refuelling the main storage tank; and unlocking and removing the fuel filling nozzle from the fuel filling receptacle, wherein the valve arrangement automatically is set in the normal operating setting.
By the provision of a fuel storage system and associated method for refuelling the fuel storage system of claims 1 and 35, increased safety against overfilling of the fuel storage system is enabled. Fuel storage systems comprising a main storage tank, an expansion tank and a valve arrangement controlling a fuel passage between the main storage tank and the expansion tank may become overfilled either if both the main and expansion tank becomes completely filled, or if the expansion tank is empty after refuelling but the fuel passage is closed, such that the fuel in the main storage tank is prevented to expand into the expansion tank.
The main function and safety feature of this invention is to prevent operating the vehicle, i.e. driving away from the filling station, when the fuel passage connecting the main tank and the expansion tank is still closed. The feature consequently makes it impossible for the vehicle to leave the filling station unless the fuel passage connecting the main storage tank with the expansion tank is open again. An open fuel passage allows fuel in the main storage tank to expand into the expansion tank upon increased fuel temperature, thereby reducing the risk for damages to the fuel storage system and/or release of fuel into the atmosphere.
According to one example embodiment, the valve arrangement may be prevented from changing setting from normal operating setting to fuel filing setting unless the fuel filling nozzle is inserted in the fuel filling receptacle. This has the advantage that the fuel passage between the main storage tank and expansion tank is not closed accidentally or by human error during normal operating setting, i.e. at times between fuel filling events. Such accidental closure of said fuel passage would prevent any fluid flow to the expansion tank and would therefore result in a safety risk.
According to a further example embodiment, the fuel storage system may further comprise a mechanical locking device located adjacent the fuel filling receptacle and configured to selectively lock the fuel filling nozzle in the fuel filling receptacle. This subject-matter represents one example embodiment for how fuel storage system is able to mechanically prevent disconnection of the fuel filling nozzle from the fuel filling receptacle under certain conditions.
According to a further example embodiment, the mechanical locking device may control the setting of the valve arrangement. That is, the actual operating position of the mechanical locking device controls the setting of the valve arrangement, such that manual or non-manual adjustment of the operating position from locked to unlocked operating position, or vice-versa, automatically may result in a change of setting of the valve arrangement. This is advantageous in view of enabling simplified handling of the fuel storage system since only the operating position of the mechanical locking device must be controlled, whilst the setting of the valve arrangement is automatic. A user does thus not necessarily need to directly control both the mechanical locking device and the valve arrangement individually.
According to a further example embodiment, the fuel storage system may compromise a mechanical linking mechanism connecting the mechanical locking device with the valve arrangement, such that the actuating position of the mechanical locking device automatically may control the setting of the valve arrangement. As mentioned above, the automatic control of the valve arrangement setting enables simplified handling of the fuel storage system.
According to a further example embodiment, the mechanical linking mechanism may automatically set the valve arrangement in the fuel filing setting when the mechanical locking device is set in a locking position. This has the advantage of reducing the risk for filling the expansion tank during refuelling, such that improved safety is realised.
According to a further example embodiment, the mechanical linking mechanism may automatically set the valve arrangement in the normal operating condition when the mechanical locking device is set in a release position. This has the advantage of reducing the risk of the vehicle driving off from the filling station with the fuel passage between the expansion tank and main storage tank in a closed state, such that improved safety is realised.
According to a further example embodiment, the mechanical locking device may be prevented from entering a locking position unless the fuel filling nozzle is inserted in the fuel filling receptacle. This has the advantage of preventing accidental or erroneous switching of the mechanical locking device into the locking position when the fuel filling nozzle is not inserted, e.g. during normal use of the vehicle, such that the flow passage between the expansion tank and main storage tank does not accidentally becomes closed during any events not being a refuelling event.
According to a further example embodiment, the fuel storage system may further comprise a locking member located at the fuel filling receptacle and configured for being actuated from a locking position to a release position by the fuel filling nozzle upon insertion thereof in the fuel filling receptacle, and the locking member may interact with the mechanical linking mechanism or the mechanical locking device such that mechanical locking device is prevented from entering a locking position unless locking member is in the release position. This subject-matter represents one example embodiment for preventing the mechanical locking device from entering a locking position unless the fuel filling nozzle is inserted in the fuel filling receptacle.
According to a further example embodiment, the locking member may be configured for being slidingly moved by the fuel filling nozzle upon insertion thereof in the fuel filling receptacle. Automatic sliding, i.e. change of operating position, of the locking member during insertion of the fuel filling nozzle enables simplified handling of the fuel storage system.
According to a further example embodiment, the locking member ma be preloaded towards the locking position by means of resilient means, such as a mechanical spring. A mechanical spring ensures a robust design and avoids an uncertain actuating position of the locking member.
According to a further example embodiment, the valve arrangement may comprise at least one moveable valve member for controlling the flow through the valve arrangement, and the mechanical linking mechanism may be connected to the at least one moveable valve member. Use of a mechanical linking mechanism for establishing the necessary control motion of the moveable valve member provides a robust, reliable and cost-effective solution that does not necessarily involve electro-mechanical components for controlling the position of the valve member.
According to a further example embodiment, the valve arrangement may comprise a three-way valve connected to the fuel filling receptacle, the main storage tank and the expansion tank, and the three-way valve may provide a fuel passage between the main storage tank and the expansion tank in the normal operating setting and a fuel passage between the fuel filling receptacle and the main storage tank in the fuel filling setting. A single three way valve having two different operating settings enables further improved user friendliness because the number of possible valve settings is reduced, and the shift between normal operating setting and fuel filling setting is realised by control of said single three-way valve.
According to a further example embodiment, the setting of the valve arrangement may be configured to be changed manually. This enables a cost-efficient and reliable system.
According to a further example embodiment, the fuel storage system may further comprise an outlet fuel line for supplying fuel to a combustion engine, and the outlet fuel line may be connected to a fuel outlet of the main storage tank. With this arrangement it is enabled to configure the fuel storage system such that fuel in the expansion tank is returned back to the main storage tank as soon as there is sufficient volume available, since the last remaining fuel in the entire fuel storage system preferably is located at the location of the fuel outlet of the fuel storage system. This is advantageous in terms of increasing the likelihood that the expansion tank is empty when refuelling occurs, i.e. when there is a low fill level in the fuel storage system, for ensuring that the required expansion space for the fuel is available when needed, that is when the fill level of the main storage tank is relatively high.
According to a further example embodiment, the expansion tank may be located higher than the main storage tank for enabling automatic return of fuel from the expansion tank to the main storage tank by means of gravitational force. This arrangement avoids the need for other more complex and expensive solutions for returning fuel from the expansion tank to the main storage tank, such as use of a fuel transfer pump.
According to a further example embodiment, the expansion tank and the main storage tank may be physically separate fuel tanks having no common side walls. This arrangement enables improved packing of the vehicle, for example in case there is a lack of space in the area of the main storage tank. The expansion tank may be located displaced from the main storage tank at a location where more space is available, and being connected to the main storage tank by means of an expansion tank fuel line.
According to a further example embodiment, the fuel storage system may further comprise a fuel feed pump, preferably submerged in the liquid fuel in the tank, for feeding fuel from main storage tank to the outlet fuel line. This arrangement reduces the risk for fuel vaporisation in the outlet fuel line.
According to a further example embodiment, the fuel storage system may be configured to store dimethylether (DME) or other similar highly volatile fuel. The low vaporisation level in terms of pressure and temperature of the fuel implies that the fuel is stored under pressure in the fuel tank, and is conveyed under pressure in the fuel lines as far as possible. Moreover, fuel cooling arrangements are preferably also included to avoid that the temperature of the fuel increases too much.
According to a further example embodiment, a solenoid shut-off valve, optionally with an automatic relief function, may be provided in a fuel line connected to the main storage tank and/or the expansion tank. Such shut-off valve may be advantageous in terms of reduced fuel vapour leakage from the main storage tank and/or expansion tank during engine standstill. The solenoid shut-off valves are configured to be set in a continuous open state during engine operating state and close only upon engine shut-down. Due to the relatively low number of opening/closing events, the sealing arrangement of the solenoid shut-off valve can be provided with a relatively soft sealing surface, such that high sealing performance can be accomplished. Thereby, also DME fuel vapour or vapour from similar fuels are effectively prevented from leaking out from the fuel tanks and migrate along the fuel lines during engine still stand. DME fuel vapour is highly volatile and tend to migrate past non-precise, worn, valves with metal sealing seats, and possibly further into various fuel components, such as fuel pumps, fuel filters, etc., thereby potentially impairing their functionality.
According to a further example embodiment, a solenoid shut-off valve with or without an automatic relief function may be provided in an expansion tank fuel line connecting the valve arrangement and the expansion tank. In case the solenoid shut-off valve comprises an automatic relief function the valve may be configured to relieve pressure in the expansion tank fuel line connecting the valve arrangement and the expansion tank, into the expansion tank.
According to a further example embodiment, a solenoid shut-off valve with or without automatic relief function may be provided in a return fuel line connected to the main storage tank and configured for returning recirculated fuel from a combustion engine into the main storage tank. In case the solenoid shut-off valve comprises an automatic relief function the valve may be configured to relieve pressure in the return fuel line connecting the engine and the main storage tank, into the main storage tank.
According to a further example embodiment, an inlet fuel line configured for supplying fuel from the valve arrangement to the main storage tank may be connected to the return fuel line at a location between the solenoid shut-off valve and the engine. Thereby, a single solenoid shut-off valve with or without automatic relief function may be used for both the return fuel line and inlet fuel line.
According to a further example embodiment, a solenoid shut-off valve with or without automatic relief function may be provided in an inlet fuel line connecting the valve arrangement and the main storage tank, which inlet fuel line may be configured for supplying fuel from the valve arrangement to the main storage tank. In case the solenoid shut-off valve is provided with automatic relief function the valve may be configured to relieve pressure in the inlet fuel line.
According to a further example embodiment, a solenoid shut-off valve with or without automatic relief function is provided in the outlet fuel line. In case the solenoid shut-off valve comprises an automatic relief function the valve may be configured to relieve pressure in the outlet fuel line connecting the engine and the main storage tank, into the main storage tank.
According to a further example embodiment, the fuel storage system may comprise a safety valve configured to open and relieve pressure from the main storage tank to the atmosphere when the pressure in the main storage tank exceeds a predetermined limit. The safety valve consequently ensures that no damages to the fuel storage system occur due to excessive fuel pressure within the fuel storage system.
According to a further example embodiment, the fuel storage system may further comprise a check and relief valve connected to the main storage tank and the inlet fuel line, wherein the check and relief valve may be adapted to allow a relief of pressure from the main storage tank to the expansion tank. This check and relief valve may be important in situations where a solenoid shut-off valve is provided in the inlet fuel line and effectively stopping fuel flow from the main storage tank to the expansion tank in the engine stillstand mode. The check and relief valve could enable fuel expansion fuel flow from the main storage tank to the expansion tank via the check and relief valve.
According to a further example embodiment, the fuel storage system comprises both a check and relief valve connected to the main storage tank and the inlet fuel line and a solenoid shut-off valve provided in the expansion tank fuel line, and both are adapted to allow a relief of pressure from the main storage tank to the expansion tank. In case a solenoid shut-off valve is provided in the expansion tank fuel line, the solenoid shut-off valve tends to prevent flow of fuel in and out from the expansion tank. However, in order to enable fuel expansion flow from the main storage tank to the expansion tank during engine stillstand, the solenoid shut-off valve in the expansion tank fuel line may be provided with an automatic relief function for enabling fuel flow from the main storage tank to the expansion tank via both the check and relief valve and the solenoid shut-off valve.
According to a further example embodiment, at least the check and relief valve, and optionally also the solenoid shut-off valve provided in the expansion tank fuel line, may be adapted to allow a relief of pressure from the main storage tank to the expansion tank at a pressure level below an opening pressure of the safety valve. This arrangement essentially enables thermal expansion caused fuel flow from the main storage tank to the expansion tank also during engine shut-down.
According to a further example embodiment, fuel storage system may further comprise a filling check valve installed in the main storage tank and connected to an inlet line configured for supplying fuel from the valve arrangement to the main storage tank, wherein said filling check valve may be adapted to open and increase the filling rate of the main storage tank when the feed pressure in the inlet fuel line exceeds a predetermined level.
According to a further example embodiment, the fuel storage system may comprise two, three or more main storage tanks, and said main storage tanks may be connected to the same valve arrangement.
It is also desirable to provide a fuel storage system for DME fuel or other similar highly volatile fuel, which fuel storage system provides reduced design complexity of the fuel storage system. According to a further aspect of the invention a fuel storage system is provided. The fuel storage system is suitable fir storing dimethylether (DME) or other similar highly volatile fuel on a vehicle. The fuel storage system comprises a main storage tank, an expansion tank, and an outlet fuel line configured for supplying fuel to a combustion engine. The outlet fuel line is connected to a fuel outlet of the main storage tank and the expansion tank is located higher than the main storage tank for enabling automatic return of fuel from the expansion to main tank by means of gravitational force. This arrangement avoids the need for other more complex and expensive solutions for returning fuel from the expansion tank to the main storage tank, such as use of a fuel transfer pump.
By the provision of the fuel storage system, any fuel expanded into the expansion tank from the main storage tank due to thermal expansion of the fuel may simply automatically flow back to the main storage tank when sufficient storage volume is available in the main storage tank. The return flow, driven by gravity force, eliminates need for additional return pumping means, such as a fuel transfer pump, and all control mechanisms associated thereto. The fuel storage system thus provides a main and expansion tank system with high reliability, high robustness and low cost, i.e. a fuel storage system with a reduced design complexity.
According to a further example embodiment, the fuel storage system may further comprise a fuel filling receptacle configured to receive a fuel filling nozzle of a filling station, and a valve arrangement having at least a normal operating setting and fuel filling setting, wherein the valve arrangement set in the normal operating setting may provide a fuel passage between the main storage tank and the expansion tank, and wherein the valve arrangement in the fuel filling setting may both provide a fuel passage between the fuel filling receptacle and the main storage tank and prevent fuel flow between the main storage tank and the expansion tank. Thereby, increased safety against overfilling of the fuel storage system is enabled.
Fuel storage systems comprising a main storage tank, an expansion tank and a valve arrangement controlling a fuel passage between the main storage tank and the expansion tank may become overfilled either if both the main and expansion tank becomes completely filled, or if the expansion tank is empty after refuelling but the fuel passage is closed, such that the fuel in the main storage tank is prevented to expand into the expansion tank. The main function and safety feature of this invention is to prevent operating the vehicle, i.e. driving away from the filling station, when the fuel passage connecting the main tank and the expansion tank is still closed. The feature consequently makes it impossible for the vehicle to leave the filling station unless the fuel passage connecting the main storage tank with the expansion tank is open again. An open fuel passage allows fuel in the main storage tank to expand into the expansion tank upon increased fuel temperature, thereby reducing the risk for damages to the fuel storage system and/or release of fuel into the atmosphere.
According to a further example embodiment, the fuel storage system may be configured to mechanically prevent disconnection of the fuel filling nozzle from the fuel filling receptacle unless the valve arrangement is in the normal operating setting. This arrangement ensures that the vehicle cannot be driven off with a closed fuel passage between the main storage tank and expansion tank.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.